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Looking for propping advice

F

firxkp

New member
Hello
Steve here. Member for a while however never posted. Looking for help and advice.
Old time boater, new to my 1995 Checkmate 253 Convincor with 454, Bravo. Love the boat. Made some mechanical repairs and runs great. Not experienced in propeller sizing. Boat does not get up on plane without some real throttle and time involved, even with full trim. Anyone with experience and advice in this topic please chime in and thanx.
 
what type of prop and pitch are you running currently? What is the WOT rpm with that prop? If you pin the stick to get on the plane, what rpm does the tach initially jump to before it starts gaining rpm?
 
Thank you for the reply Glenn. Steve Kotraba here. Purchased the Checkmate out of an estate. Owner has passed away and wife had a broker with no knowledge of its history handling sale. Wife could not speak to maintenance history. Boat is currently in harbor shop having what turned out to be original 1995 injectors replaced. Also found both fuel pumps were original 1995. Was discovered both were weak and had overall 10 pounds less fuel pressure than specification, both replaced.
Prop is 4 blade stainless with markings indicating 14.75 x 24P, Hydromotive Intimidator quad IV. HC-CL24R-Q-IV
Prior to putting in for service I had ran the boat a couple of times and found it to run smoothly and could get it up on plane by applying full throttle and using steering, left to right rocking would get the bow down, but not proficiently. Because I have never had propping issues in prior boats I did not take note of initial 'pinning of stick' rpms during these trials. A lesson learned and I thank you. When I get the boat out of shop I will watch these indicators. However I am able to say after she crawled out of the hole, I noted a top speed of 65-68 mph at approximately 5000 rpm.
These sea trials where generally with almost full fuel, which is 75 gallon in this model, no cargo, usually just me, at 185 pound.
I am not looking for top end extreme speeds. I would like to see the best hole shot possible.
I do appreciate your time and hope this bit of information assists in whatever advice you may have to offer.
 
I don't think that prop sounds off. That's a pretty popular prop and pitch for your current set up. Might want to have a compression test or leak down test performed.
 
Was the speed GPS based or just a pitot tube speedometer? If I use 67 mph actual (GPS based) and a 1.5 gear ratio in the Bravo, you have 12% slip which is not bad for that hull. People that own the same hull/engine/drive combo will hopefully chime in. If the actual GPS speed was really more like 63 mph the slip would be closer to 17% and then a prop change might improve it.
75 gallons of non ethanol gas is about 450 lbs and all of that near the back will slow it coming on the plane. Were the rpm / speed values after the injectors and fuel pumps were replaced or before? You want to make sure that the both the rpm and speed (GPS) are correct readings and I only assumed you have a 1.5 drive ratio. I also assume that at WOT you kept trimming the drive out as long as the speed kept picking up. The previous post suggested you check the compression and leak down, and if not already done so, I would check for full WOT, proper timing, new cap, wires and rotor if they are not in good shape. IF the engine checks out healthy, I would try to get my hands on 23P or 24P Bravo FS prop to try if possible. A 24P Bravo FS is really about 23.4P and the 23P FS is closer to 22.3P. That willl also raise the WOT rpm a bit. I think the Hydro is more of a stern lifting prop. The Bravo FS is more of a bow lifting prop, while the standard Bravo prop is more stern lifting. On my boat a 26P Bravo actually planes a bit faster than a 24P Bravo FS due to the diffuser on the barrel of the standard Bravo prop. However, the Bravo FS has more top end and less slip on my hull and still planes very quickly. Not sure which version your hull will like best. Hopefully more members with your combination will chine in on the prop they have found best. I assume you came on the plane with the drive trimmed in all the way?
 
Glenn Kornett said:
Was the speed GPS based or just a pitot tube speedometer? If I use 67 mph actual (GPS based) and a 1.5 gear ratio in the Bravo, you have 12% slip which is not bad for that hull. People that own the same hull/engine/drive combo will hopefully chime in. If the actual GPS speed was really more like 63 mph the slip would be closer to 17% and then a prop change might improve it.
75 gallons of non ethanol gas is about 450 lbs and all of that near the back will slow it coming on the plane. Were the rpm / speed values after the injectors and fuel pumps were replaced or before? You want to make sure that the both the rpm and speed (GPS) are correct readings and I only assumed you have a 1.5 drive ratio. I also assume that at WOT you kept trimming the drive out as long as the speed kept picking up. The previous post suggested you check the compression and leak down, and if not already done so, I would check for full WOT, proper timing, new cap, wires and rotor if they are not in good shape. IF the engine checks out healthy, I would try to get my hands on 23P or 24P Bravo FS prop to try if possible. A 24P Bravo FS is really about 23.4P and the 23P FS is closer to 22.3P. That willl also raise the WOT rpm a bit. I think the Hydro is more of a stern lifting prop. The Bravo FS is more of a bow lifting prop, while the standard Bravo prop is more stern lifting. On my boat a 26P Bravo actually planes a bit faster than a 24P Bravo FS due to the diffuser on the barrel of the standard Bravo prop. However, the Bravo FS has more top end and less slip on my hull and still planes very quickly. Not sure which version your hull will like best. Hopefully more members with your combination will chine in on the prop they have found best. I assume you came on the plane with the drive trimmed in all the w
Click to expand...
 
Thank everyone for the great information. I can tell it comes from a wealth of knowledge and experience.
The mechanic is predisposed with a family member in hospice for cancer and as you would do, I will not bother him until a better time. However once available I will have several questions based on the information presented in your comments.
Compression check was undertaken and all cylinders were within 10-15 % of each other within specification.
I did continue to trim out of a full down trim as she came up on plane, and enjoyed performance once on top. Speed was pitot based and then GPS with about a 3 mph difference between. I too am uncertain of the drive ratio. A question for the wrench. All other items noted have been updated including wires plugs. Is electronic ignition.
Can't recall if prop has vent holes. Please inform how opening them will benefit. Again, I have limited prior propping experience.
I will close with an expression of gratitude to all and blessings.
Thanx
SMK
 
firxkp said:
Thank everyone for the great information. I can tell it comes from a wealth of knowledge and experience.
The mechanic is predisposed with a family member in hospice for cancer and as you would do, I will not bother him until a better time. However once available I will have several questions based on the information presented in your comments.
Compression check was undertaken and all cylinders were within 10-15 % of each other within specification.
I did continue to trim out of a full down trim as she came up on plane, and enjoyed performance once on top. Speed was pitot based and then GPS with about a 3 mph difference between. I too am uncertain of the drive ratio. A question for the wrench. All other items noted have been updated including wires plugs. Is electronic ignition.
Can't recall if prop has vent holes. Please inform how opening them will benefit. Again, I have limited prior propping experience.
I will close with an expression of gratitude to all and blessings.
Thanx
SMK
Click to expand...
Good, it sounds like the engine is in good health and you trimmed it for maximum speed without overtrimming. If the prop has vent holes and you open them up, it allows exhaust gases into the blades, which will result in the prop spooling up faster and raising the engine rpm when you pin the stick. This allows an engine that would normally not spool up quickly (prop a bit too hard to turn at low rpm) to get into the powerband faster and help get the boat on the plane faster if, and I say if, the prop just won't spool up fast enough without doing that. On the flip side, if the prop does spool up fast enough, additional venting will increase the slip and make it more difficult to get on the plane, and in those cases closing the prop vents will help. I would still try and get my hands on a 23P or 24P Bravo or Bravo FS and try it first with all the vents closed. The only why to find out is to try, just like we all did the first time we had to deal with the same issue. Stay at it and you will get it right.
 
Glenn Kornett said:
Good, it sounds like the engine is in good health and you trimmed it for maximum speed without overtrimming. If the prop has vent holes and you open them up, it allows exhaust gases into the blades, which will result in the prop spooling up faster and raising the engine rpm when you pin the stick. This allows an engine that would normally not spool up quickly (prop a bit too hard to turn at low rpm) to get into the powerband faster and help get the boat on the plane faster if, and I say if, the prop just won't spool up fast enough without doing that. On the flip side, if the prop does spool up fast enough, additional venting will increase the slip and make it more difficult to get on the plane, and in those cases closing the prop vents will help. I would still try and get my hands on a 23P or 24P Bravo or Bravo FS and try it first with all the vents closed. The only why to find out is to try, just like we all did the first time we had to deal with the same issue. Stay at it and you will get it right.
Click to expand...
Thank you again. I will continue research and follow up as we progress.
 
When considering the Bravo, do we stay with the 14.75 diameter or does the change down to 23 in pitch require change in diameter ?
 
firxkp said:
When considering the Bravo, do we stay with the 14.75 diameter or does the change down to 23 in pitch require change in diameter ?
Click to expand...
As far as I know all Bravo series props are 15.25" diameter including the Bravo 1, Bravo FS, Bravo XS and XC. I think the actual diameter is closer to 15.125" but Merc lists them as 15.25".
 
vent holes usually are for outboard engines to get engine RPM into power band. really don't need them on IO's because of engine torque. I tried bravo-1 4B and presently running Hydromotive Intimidator quad IV-X per their advise. I tried Bravo-1 and just like the hydromotive better. Give them a call.

Marine Propellers, Stainless Steel Boat Propellers

Hydromotive Engineering Company was established in 1980 to provide aftermarket products to the performance boating industry, with a specialty in high performance stainless steel propellers and related components designed to reduce gear case drag and improve propulsion efficiency. With over...
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Just some wild speculation here, but sounds to me like the current prop is for max top speed, and going down an inch or two on a the pitch might get it on plane faster at the cost of higher rpm and/or lower top speed. Any trim tabs on your boat to push the stern up?

I switched from a 21 Mirage to a 23 Mirage Plus on my 88 Formula 24' (330HP 454 Bravo 1) this year and while my top speed stayed the same at around 51 mph, the cruising rpm dropped by 400, and down 600 (to 4500) at max speed. Takes longer to get on plane now, too, but not long enough to be concerned. All in all happier with my new prop.
 
My gratitude for all the advice. Hope to have new injectors installed this week, follow up with mechanic on leak down test results and determine if a head gasket may be called for. Staying with current prop for time being, considering pitch advice all around. Have trim tabs and have always believed lower unit trim was all that was needed, but the concept of stern lift makes a whole lot of sense. Thanx. No vent holes in current prop.
 
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